WASHINGTON — In their debates so far, the Democratic presidential candidates haven’t yet grappled with a question that affects a traditional Democratic constituency: low-income workers.

The question: Do immigrants and foreign guest workers lower the wages of Americans at the bottom end of the income scale?

The immigration bill which the Senate is debating this week is a series of compromises among a bipartisan group of senators.

Democrats who support the bill know that, in order for it to hold together, they’ll have to accept some form of guest worker plan.

But Tuesday on the Senate floor one Democrat, Sen. Byron Dorgan of North Dakota, and one independent who lines up with Democrats, Sen. Bernie Sanders of Vermont, passionately made the case that a new guest worker program would lower Americans’ wages.

Attempt to kill guest worker proposal
Dorgan tried to kill the guest worker provision in the bill that would, at first, allow 400,000 temporary workers per year to enter the United States, with annual adjustments in the number based on labor market demand.

Instead of framing immigration as an ethnic issue or one of national security, Dorgan and Sanders re-framed it as a matter of economic class and equity.

Dorgan said he was speaking on behalf of low-wage American workers, "the people you don't see very often, they are the people who pass the coffee to you across the counter or help out at the gas station and do those kinds of jobs... They are going to have to shower after work because they work hard and they sweat and they do not get paid very much."

Citing one industry, Dorgan said 86 percent of the people who work in food preparation are Americans or legal permanent residents.

“If you want to bring in people at the bottom of the economic ladder, low-wage workers, you know what that does to the other 86 percent…. It puts downward pressure on income. We don't have to debate about that. That debate is over,” he told senators.

Sanders said, “At a time when millions of Americans are working longer hours for low wages and have seen real cuts in their wages and benefits, this legislation would… bring millions of low-wage workers from other countries into the United States. If wages are already this low in Vermont and throughout the country, what happens when more and more people are forced to compete for these jobs?”

Sanders denounced U.S. corporations which he said were “pushing legislation which displaces American workers and lowers wages in this country by bringing low-wage workers from abroad into America.”

Sen. Barbara Boxer, D- Calif., also spoke in support of Dorgan's effort.

Adjust number of workers to demand
A leading Republican supporter of the bill, Sen. Jon Kyl of Arizona, tried to rebut the Dorgan-Sanders arguments.

“With an adjustable temporary worker visa, you adjust it to the needs at the moment — to the demand for labor. As your construction boom goes up and you need more labor, you have more visas,” Kyl told reporters. “As you go down and don’t need as many homes to be constructed, you don’t issue as many visas. So you have the market being able to work and the wages rising and falling based on market conditions, rather than an artificial glut of labor.”

But what if the foreign workers decide to stay in the United States at the end of their two-year legal stint and melt into the U.S. population?

Kyl answered that question with a question of his own: “Could somebody survive in this country by always being able to find day labor or be employed by somebody out in the middle of Montana with the government never auditing the employer? That’s theoretically possible, but very difficult.”

Kyl contends that the federal government’s new process of checking on employers and their workers’ legal status will be thorough enough to catch illegal workers and punish those who hire them.

Dorgan’s bid to kill the guest worker program lost on a vote of 31-64, with 18 of his fellow Democrats voting against him.

Only two Republicans, Sen. David Vitter of Louisiana and Sen. Tom Coburn of Oklahoma, voted with Dorgan.

With safe seats in the Senate, Dorgan and Sanders can afford to raise the awkward guest worker issue. Sanders, just elected last November with 65 percent of the vote, will probably hold his seat until he chooses to retire. Dorgan, in his third term as a senator, has never been defeated since he won a seat in the House in 1980.

On Thursday, by a vote of 74 to 24, the Senate approved an amendment offered by Sen. Jeff Bingaman, D- N.M., to cut the annual guest worker number to 200,000.

Effect of legalizing the illegal workers
If guest workers depress wages of Americans, as Sanders and Dorgan contend, does the same logic also apply to the estimated 12 million illegal immigrants now in the United States who’ll become legalized members of the labor force if the bill becomes law?

In an interview after Tuesday night’s vote, Sanders took an equivocal position on the potential wage-lowering effect of legalizing the 12 million.

“They are part of the labor force now, that’s why they’re here. The question is whether we want to make a difficult situation even worse.”

He added, “I am concerned in general that wages in the United are going down for millions of workers… illegal immigration has a lot to do with it, the decline of unions has a lot to do with it and a number of other factors.”

He would not say whether he’d vote for the immigration bill, once the Senate finishes amending it.